Method of continuous casting with circular trough mold

ABSTRACT

A generally horizontal annular trough forming a circular mold cavity is rotated about a generally vertical axis to transfer molten metal from a feeding station through a solidifying zone and thence through a discharge station where the solidified metal is continuously removed from the mold. The solidifying zone is formed by a cooling station including means for continuously cooling the trough to solidify molten metal in the mold, and a hood overlying at least part of the cooling station forms a substantially enclosed space above the open top of the mold. This space contains nozzle means for concentrating on the upper surface of the metal a stream of non-oxidizing gas which, prior to complete solidification of the metal, forms a solidified skin across its upper surface to prevent escape of gas from within the metal. Thus, when the metal is of the type that evolves gas to offset shrinkage during solidification, the upper surface of the solidified casting is flat rather than concave.

United States Patent Yearley 3,682,228 51 Aug. 8, 1972 [54] METHOD OF CONTINUOUS CASTING WITH CIRCULAR TROUGI-I MOLD Douglas c. Yearley, Westfield, NJ.

Assignee: Phelps Dodge Copper. Products Cor- V poration, New York, NY.

Filed: March 11, 1971 Appl. No.: 123,236

Related U.S. Application Data Division of Ser. No. 647,680, June 2l, 1967, Pat. No. 3,603,378.

Inventor;

US. Cl ..-.....l64/l24, 164/82 Int. Cl. ..B22d 11/00 Field of Search ..164/259, 82, 72, 83,88, 268,

References Cited UNITED STATES PATENTS 2,099,208 ll/l937 Horsfall ..l6 4/259 3,284,859 ll/l966 Conlon ..164/259 Primary Examiner .l. Spencer Overholser Assistant Examiner-John S. Brown Attorney-Davis, Hoxie, Faithful] & Hapgood ABSTRACT A generally horizontal annular trough forming a circular mold cavity is rotated about a generally vertical axis to transfer molten metal from a feeding station through a solidifying zone and thence through a discharge station where the solidified metal is continuously removed from the mold. The solidifying zone is formed by a cooling station including means for continuously cooling the trough to solidify molten metal in the mold, and a hood overlying at least part of the cooling station forms a substantially enclosed space above the open top'of the mold. This space contains nozzle means for concentrating on the upper surface of the metal a stream of non-oxidizing gas which, prior to complete solidification of the metal, forms a solidified skin across its upper surface to prevent escape of gas from within the metal. Thus, when the metal is of the type that evolves gas to offset shrinkage during solidification, the upper surface of the solidified casting is flat rather than concave.

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SHEET 3 (IF 3 INVENTOR. 001/644: 6. l-mzsr BY I ll'lllllfil METHOD OF CONTINUOUS CASTING WITH CIRCULAR TROUGH MOLD This application is a division of my application Ser. No. 647,680 now Pat. No. 3,603,378, filed June 21, 1967. I

This invention relates to casting with apparatus of the type in which the molten metal is continuously fed from a supply station into a mold consisting essentially of a circular trough rotating about a generally vertical axis of the circle, whereby the metal solidifies as it is carried by the rotating trough to a discharge station which removes the metal continuously as a rod, or the I like.

An apparatus of the above-mentioned type affords numerous advantages, particularly in the improved form disclosed in U.S. Pat. No. 3,284,859 granted Nov. l5, 1966. In the apparatus disclosed'in said patent, the metal is solidified in a cooling zone or station through which the mold rotates, and an overlying hood forms a substantially enclosed space in which a protective atmosphere of nonoxidizing gas is maintained to minimize absorption of oxygen by the solidifying metal. However, this manner of solidification leaves much to be desired when the metal is of the type in which gas evolution during solidification can be controlled to offset shrinkage. More particularly, with that type of metal the solidification results in a concave surface on the top of the discharged casting, making it quite unsuitable for hot rolling.

The principal object of the present invention is to provide a continuous casting method of the character hood has anoutletlocated between the nozzle and feeding station and to which the stream passes countercurrently to the movement of molten metal by the rotating mold.

The invention is described in more detail hereinafter with reference to the accompanying drawings, in which:

FIG. 1 isa plan view of a preferred form of the new apparatus;

FIG. 2 is a side elevational view, partly in section, of the apparatus illustrated in FIG. 1, showing details of the molten metal feeding meansand part of the hood overlying the cooling zone;

FIG. 3 is a view similar to FIG. 2 but showing a different portion of the hood and the nozzle means therein; and

described in which the upper surface of the discharged casting is flat, so that the casting is well adapted for hot rolling.

The method of the present invention is concerned with metals (including metal alloys) of the type adapted to generate a controlled quantity of gas during solidification to offset the solidification shrinkage, for example, oxygen-bearing copper commonly known as tough pitch copper. l have found that in casting such metals with the aforesaid prior apparatus, the enclosed protective atmosphere overlying the rotating mold prevents convective cooling of the top surface of the metal so that solidification proceeds from the bottom toward the top, and all the evolved gas passes through the molten metal pool into the atmosphere, the resulting shrinkage causing the undesired concave shape of the upper surface of the casting.

According to the invention, the substantially enclosed space within the hood at the cooling zone contains nozzle means connected to a source of pressurized non-oxidizing gas, and the nozzle means are disposed to concentrate a stream of the gas upon the upper surface of the molten metal in the rotating mold. The nozzle means are so dimensioned and located as to direct the gas stream at a'flow rate and position to form, by convective cooling, a solidified skin across this upper surface which entraps the gas bubbles evolved as solidification of the underlying metal proceeds. The gas bubbles thus entrapped form discrete pores within the casting predominately near its upper surface, the volume of these pores serving to offset solidifying shrinkage so that the desired flat upper surface of the casting is obtained.

For best results, the nozzle means include at least one nozzle directed toward the feeding station; and the FIG. 4 is a sectional view on the line 44 in FIG. 3.

Referring to FIG. 1, the continuous casting apparatus there shown comprises a stationary vertical post or axle 20 extending through a hub 21 having a close rotating fit on the axle. Hub 21 is adapted to be rotated on the axle at constant speed by a motor 22 connected through a variable speed transmission 23 and shaft 23 to a bevel gear 25 meshing with a large bevel gear 26, the latter being secured to hub 21.

The hub 21 has rotating spokes 28 secured at their outer ends, as by welding, to an annular trough 29 having a circular mold cavity 29a which is open at the top. The ring-shaped trough 29 is supported on horizontal rollers 30 spaced around the vertical axle 20 and mounted on suitable stationary supports (not shown).

The motor 22 operates through hub 21 and spokes 28 to rotate the annular trough 29 about the vertical axle 20 as an axis. For simplicity and to avoid duplication, only some of the rollers 30 are illustrated, it being understood that they are provided in sufficient number to support the circular trough 29 in a horizontal position when it is rotated and loaded with the casting metal. 1

The molten metal is fed continuously into the rotating mold cavity 29a by feeding means shown generally at 32 in FIG. 1. The mold rotates counter-clockwise as viewed in FIG. 1, thereby carrying the metal from the feeding means 32 through an overlying gas-applying station 33 where the metal is subjected on its exposed upper surface to a non-oxidizing gas while being cooled by water sprayed against the outside of the trough 29 from stationary nozzles 65 spaced along the trough. These nozzles form a cooling station or zone and are continuously supplied with cooling water from a supply source (not shown) through tubes 66, the spent cooling water descending from the trough being collected in any suitable manner. Continued rotation of the mold carries the solidified metal to a cast metal discharge station 34, where it is continuously discharged from the mold. As the mold continues to rotate from discharge station 34, it may pass through stations (not shown) for preheating and dressing the mold before it reaches the feeding means 32. The details of the discharge station 34 and the preheating and dressing stations may be as disclosed in the aforementioned U.S. Pat. No. 3,284,859.

Referring now to FIG. 2, the feeding means 32 comprise a pouring cup 36 preferably having a lining of refractory material. The cup 36 forms a main chamber 37 open at the top for receiving molten metal from a launder 38 or other source. The pouring cup also has an overflow weir 39 over which the main chamber 37 communicates with a discharge ,spout 40 of the cup. The spout 40 has an entrance end 40a which receives the molten metal from the overflow weir 39 by way of a stantially equal to the width of the mold cavity 29a.

The pouring cup 36 is supported by means comprising a pair of graphite shoes 42 and 43 seated on the bottom of the mold cavity 29a and each having a sliding fit in thiscavity. The shoes are secured to the bottom of cup 36, by means including bolts 42a and 43a, respectively, for connecting the shoes to depending flanges 36a of the cup. The front shoe 42 is located adjacent the discharge end 40b of the spout and has a close sliding fit in the mold cavity 29a.so as to form a dam for preventing reverse flow of the molten metal entering the cup against movement by rotation of the trough.

while allowing free movements of the cup vertically and laterally.

As shown in FIG. 2, the pouring cup 36 is located closely adjacent the gas-applying station 33, which comprises a hood 50 overlying the trough 29 and held stationary by a suitable support 51 (FIG. 1). The hood 50 has depending side walls which lie closely adjacent opposing side walls of trough 29 (FIG. 4), whereby the hood forms a substantially enclosed space 50a above the mold cavity 290.

Within the hood space 504i is a manifold 53 extending lengthwise of the mold cavity 29a and directly above it, as shown in FIGS. 3 and 4. The manifold is As shown in FIG. 2, the top of hood so is provided with a view port covered by a sight glass' 60. The latter is located near the pouring cup 36 to enable inspection of the molten metal as it is delivered into the mold from spout 40, which extends into the rear end of the hood. Between the sight glass 60 and the pouring cup 36, the top of hood 50 is provided with an outletport 61 for discharge of gas supplied by the nozzle means 54.

The nozzle means 54 are located a sufficient distance beyond the feeding spout 40 to allow the molten metal in the mold to quiesce before its upper surface is subjected to the streams of non-oxidizing gas from the nozzles. However, the nozzle means 54 are so positioned in relation to the cooling means 65-66 that the interior of the body'of molten metal has not solidified by the time its upper surface is subjected to the action of the jets from nozzles 54. The dimensions of the nozzle means 54 and the adjustment of valve 57 are such that the strearm of non-oxidizing gas are concentrated upon the upper surface of the molten metal at a flow rate suffi- I cient to solidify this upper surface prior to complete solidification of the metal in the mold. Thus, a solid, flat metal skin is formed at the upper surface of the metal by convection cooling; and solidification of the metal then proceeds from the bottom and sides as well as the top, with the result that the metal casting discharged at the station 34 (FIG. 1) has a flat upper surface as well as being flat at the sides and bottom. Such a casting is well adapted for hot rolling.

The above-mentioned convection cooling, under the conditions as described, has the effect of sealing the upper exposed surface of the incompletely solidified metal and thereby preventing escape of gas from the interior of the metal, which would cause the upper surface to take a concave form as solidification of the provided with nozzle means comprising a plurality of depending nozzles 54 having their discharge ends located close to the upper. surface of the metal in the mold. As shown, there are four such nozzles 54 spaced length-wise of the underlying mold cavity and extending downwardly and rearwardly toward the feeding sta tion 32, so that the discharge from each nozzle is directed against the upper surface of the metal countercurrently to the direction of its travel in the mold.

The manifold 53 is securedto and supplied from the lower end of a tube 55 extending through the top of.

metal continues;

As an example of the location of the nozzle means 54 i to attain the above described results, such means may be located about two feet beyond the feeding spout 40b when the circular mold cavity 29a has a diameter of 15 feet. Also by way of example, the valve 57 may be adjusted to maintain a gas pressure of about 10 pounds per square inch in the manifold 53.

It will be understood that the gas delivered from the nozzles 54 for the convection cooling heretofore described also maintains a non-oxidizing atmosphere in the hood space50a, to prevent absorption of oxygen by the metal while it is solidifying. This atmosphere as a whole moves slowly in the direction countercurrent to the movement of the mold, that is, toward the gas outlet 61. While I prefer-that the gas nozzles 54 be inclined as shown in FIG. 3, it is to be understood that they may be directed straight downwardly or otherwise, provided that they concentrate their jets of gas upon the upper surface of the metal in the mold so as to solidify that hood 50, the tube being mounted in a suitable fitting 56 60 surface by convection cooling.

The feeding means 32 for the molten metal, as shown in FIG. 2, are preferred but form no part of the present invention.

To illustrate the effect of the present invention, tough pitch" copper was continuously cast into a bar having a cross-sectional area of four square inches, at a rate of 30 feet per minute. When the gas flow through the nozzle means 54 was interrupted, the upper surface of the casting promptly became concave; but when the gas flow was resumed, this cast surface returned to its flat or level shape.

I claim:

1. In the continuous casting of metal of the type which, during solidification, is adapted to evolve gas in an amount controllable to offset shrinkage, the method which comprises the continuous steps of rotating-a circular mold about a generally vertical central axis, introducing molten metal into the mold at a feeding zone, cooling the mold in a cooling zone to solidify metal from said feeding zone, forming a solidified skin across the entire upper surface of the metal by directing a flow of non-oxidizing gas upon said upper surface, said 

1. In the continuous casting of metal of the type which, during solidification, is adapted to evolve gas in an amount controllable to offset shrinkage, the method which comprises the continuous steps of rotating a circular mold about a generally vertical central axis, introducing molten metal into the mold at a feeding zone, cooling the mold in a cooling zone to solidify metal from said feeding zone, forming a solidified skin across the entire upper surface of the metal by directing a flow of nonoxidizing gas upon said upper surface, said solidified skin formation being effected at a region of the cooling zone where the metal below said surface remains substantially unsolidified, thereby entrapping gas bubbles evolved in the metal as its solidification proceeds in the cooling zone, and discharging the solidified metal from the rotating mold.
 2. The method according to claiM 1, which comprises also maintaining a substantially enclosed atmosphere of the non-oxidizing gas at the upper surface of the metal in said cooling zone.
 3. The method according to claim 1, in which said metal is tough pitch copper. 